For factory test, the diagnosis is usually performed in a microwave anechoic chamber where the wireless environment can be precisely controlled.
Therefore, the channel vectors \(\mathbf {h}_\mathrm {RX}\)  and \(\mathbf {h}_\mathrm {TX}\)  can be calculated based on known spatial coordinates [1]}, [2]}, [3]}.
In this case, the wireless channel can be simplified as the free-space transmission model, where \(L_\mathrm {TX} = L_\mathrm {RX} = 1\)  and all channel parameters in (REF ) are available.
In this way, the channel can be obtained without channel training.
